1. Technical Field
The present disclosure relates to a biosignal determining device and biosignal determining method for measuring biological impedance by using a plurality of electrodes attached onto the body of a user and for extracting information regarding respiration.
2. Description of the Related Art
A method of extracting respiratory information from thoracic impedance in low electrical current (10 nA) is disclosed in Jeffry Bonar Fernando, et al., “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”, International Conference of the IEEE Engineering in Medicine and Biology Society, pp. 3829-3832 (2013).
Prior to describing the concept of the method described in the above cited document “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”, basic components of cardiography are described. FIG. 1 depicts basic components of cardiography in one cycle. The cardiography has peaks called a P wave, a Q wave, an R wave, an S wave, and a T wave. A portion of each of QRS waves represents excitation of the ventricles.
FIG. 2A to FIG. 2C represent a concept of the method described in the above cited document “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”. At measurement, four electrodes are attached onto the center of the chest (refer to FIG. 2A). In FIG. 2A, except an electrode to establish a ground, inner two of four electrodes in line are used to measure a potential. Between two outer electrodes, a low electrical current (10 nA) is caused to flow. FIG. 2B depicts thoracic impedance measured from the potential. In the above cited document “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”, the envelope of the T wave as a cardiography-derived component is referred to as a respiration curve, and the respiration curve is assumed to include respiratory information.
In the above cited document “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”, thoracic impedance is measured by attaching four electrodes onto the center of the chest. In an experiment described in the above cited document “Estimation of respiratory signal from thoracic impedance cardiography in low electrical current”, a subject was made to perform breathing in four phases, that is, “normal breathing”, “deep breathing”, “no breathing”, and then “normal breathing”. The subject was instructed to perform normal breathing in a cycle of three seconds fifteen times, perform deep breathing in a cycle of five seconds eight times, and stop breathing for thirty seconds.
FIG. 2C depicts respiration extraction results. The cycle in the envelope is correlated with actual breathing. Since the amplitude in no breathing is extremely small and the amplitude in deep breathing is larger than the amplitude in normal breathing, the extracted respiratory information represents actual breathing.